318 Chrysler V8 problems

[LRT]

We have a Dodge AT4 575 truck with a 318 Chrysler V8. At approximately 50°C, or after 5 minutes smooth running without choke, the engine starts to lose speed at idle and misses and pinks. Then, apart from occasionally backfiring, it does not respond to the throttle.

When connecting the vacuum gauge whilst the engine is cold, the vacuum gauge states everything is normal. However, when the engine starts to warm up, the vacuum steadily disappears as if the engine was turned off. Adjusting the ignition timing makes no difference.

We have replaced the vacuum hose to the distributer, the ignition leads and plugs, the ignition coil, and the distributer cap, and the engine still wont run properly at operating temperature.

Does anyone know what may be wrong?

LRT

[PhilipA]

Do these have a hot spot under the carby? if so maybe it has rusted through .
Regards Philip A

[langy]

One thing to check - loose intake manifold bolts &/or manifold gasket expired. Otherwise, you may have a vacuum hose connected the wrong way in the emissions setup (If it even has such stuff ). Make sure the dissy is hooked up to the correct port on the carby ( I've done such a thing myself).

Spraying around carby cleaner at places that are suspect for vacuum leaks also works ( But it has it's hazards....)

[LandyAndy]

Langy is onto it.
Best way to find the problem is with a CRC spray(use the plastic tube) if there is a gasket leak the engine revs will pick up when it sucks the extra fuel (CRC) in.
Only spray small amounts at a time as there is a posibility of ignition of the spray from arcing plug leads.
GOODLUCK
Andrew

[LRT]

Hi PhilipA, the inlet manifold is rusty, but appears to be sound. However, I will check further. Thanks for the advice. LRT

[LRT]

Hi langy, the vacuum hose is only from the carbureter to the distributer, with no emission system. However, I will check the intake manifold and gasket.
LRT

[LRT]

Hi LandyAndy, do you remove the air cleaner and spray it down the carby? Or do you just spray it around the manifold? LRT

[bee utey]

Have a listen to the exhaust as the engine is dying. Maybe there's damage inside the muffler or you may have a faulty heat flap in the exhaust manifold. You would get a hissing noise (Valiant vacuum cleaner noise). Ripping the exhaust off may help.

I assume by your first post that the ignition is electronc as you don't mention points. The chrysler electronic ignition can fail in the same way the Lucas system in the LR systems. In fact I did my Bosch amp conversions on them long before the landies. If it's points your condenser may not like you.

[LandyAndy]

Hi LandyAndy, do you remove the air cleaner and spray it down the carby? Or do you just spray it around the manifold? LRT

Spray it around the carby base(gasket) then around the intake manifold gaskets where it joins the heads.
Its the easiest way to find leaking gaskets.
Andrew

[Davehoos]

a 360 2 barrel i worked on had an exhaust port into the intake manifold that has no control valve-im assuming its open at all time and exhaust pressure changes the amount of gases through.

has these engines got a vac hose into the auto choke mechanism.

[LRT]

Hi bee utey, the engine does make a hissing sound. The distributer doesn't have points.

Furthermore, when the engine warms up the fuel-air mixture goes straight out the exhaust, with the engine just running at about 100revs. When you try to accelerate the engine it pops back thru the intake manifold and pinks and stutters, then the revs gradually slow down until it stops running with no response from the throttle.

When cold, the engine runs well and is very responsive to the throttle, but quickly snapping open the throttle causes it to pop back thru the intake manifold.

LRT

[LRT]

Thanks LandyAndy for the locations to spray the CRC Carby cleaner. LRT

[LRT]

Hi Davehoos, this engine only has a manual choke. LRT

[bee utey]

If the engine has a mechanical fuel pump the diaphragm may have holed and you may have a sump full of petrol (I've met this more than once!). As it warms up the petrol evaporates more and more and floods the engine. Lift the oil filler cap and sniff for petrol. Look at the dip stick and check for excessive level. You might have to run it on an electric fuel pump instead, after draining the sump and refilling.

[LRT]

Bee utey, I think your right. The rocker cover oil fill smells of only pure oil, but the oil on the dip stick does have a hint of fuel in it.

This engine problem only occurred a few days later after changing the engine oil and filter. Could this be related to the problem?

The carby fitted is a Carter Carburettor, made in USA.

What size or capacity electric fuel pump should we install?

LRT.

[bee utey]

Bee utey, I think your right. The rocker cover oil fill smells of only pure oil, but the oil on the dip stick does have a hint of fuel in it.

This engine problem only occurred a few days later after changing the engine oil and filter. Could this be related to the problem?

The carby fitted is a Carter Carburettor, made in USA.

What size or capacity electric fuel pump should we install?

LRT.
The timing is probably a coincidence. Fuel pumps let go when they feel like it. Simply using the engine more after a service is enough.

As for a replacement pump, I regularly used Facet brand electronic fuel pumps on V8 dual fuel (carby) cars because of the chance of failure of the engine driven pump is too high. Can't remember the correct part numbers but your local auto store should have a catalogue with recommended pump listings.